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We constantly hear that we’re on the verge of an AI revolution, but the technology is already everywhere. And Coursera co-founder Andrew Ng predicts that smart technology will help humans do even more. It will drive our cars, read our X-rays and affect pretty much every job and industry. And this will happen soon.

As AI rises, concerns grow about the future of humans. So how can we make sure our economy and our society are ready for a technology that could soon dominate our lives?

And why wouldn’t there be? One of the smartest humans alive, Stephen Hawking, says AI could end mankind.

But the question isn’t whether to worry about AI, it’s what kind of AI to worry about.

Tesla founder Elon Musk recently warned a gathering of governors that they need to act now to put regulations the development of artificial intelligence. “I keep sounding the alarm bell, but until people see robots going down the street killing people, they don’t know how to react, because it seems so ethereal,” he said.

Musk is not talking about the sort of artificial intelligence that companies like Google, Uber, and Microsoft currently use, but what is known as artificial general intelligence — some conscious, super-intelligent entity, like the sort you see in sci-fi movies. Musk (and many AI researchers) believe that work on the former will eventually lead to the latter, but there are plenty of people in the science community who doubt this will ever happen, especially in any of our lifetimes.

To understand the threats AI may or may not pose to society, it’s best to understand the types of AI that do and don’t (yet) exist. Wait But Why has a great summary:

AI Caliber 1) Artificial Narrow Intelligence (ANI): Sometimes referred to as Weak AI, Artificial Narrow Intelligence is AI that specializes in one area. There’s AI that can beat the world chess champion in chess, but that’s the only thing it does. Ask it to figure out a better way to store data on a hard drive, and it’ll look at you blankly.

AI Caliber 2) Artificial General Intelligence (AGI): Sometimes referred to as Strong AI, or Human-Level AI, Artificial General Intelligence refers to a computer that is as smart as a human across the board—a machine that can perform any intellectual task that a human being can. Creating AGI is a much harder task than creating ANI, and we’re yet to do it. Professor Linda Gottfredson describes intelligence as “a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience.” AGI would be able to do all of those things as easily as you can.

AI Caliber 3) Artificial Superintelligence (ASI): Oxford philosopher and leading AI thinker Nick Bostrom defines superintelligence as “an intellect that is much smarter than the best human brains in practically every field, including scientific creativity, general wisdom and social skills.” Artificial Superintelligence ranges from a computer that’s just a little smarter than a human to one that’s trillions of times smarter—across the board.

Type 1 exists. This is what we use every day. This is what is reshaping our social networks, advertising and economy. The threat here is already visible. “Fake news” designed to hoax humans games algorithms to reach a wider audience. Automation is replacing human jobs.

Types 2 and 3 cause the anxiety. Futurist Michael Vassar, who has worked with AI, has used Nick Bostrom’s thinking on artificial intelligence to predict that “if greater-than-human artificial general intelligence is invented without due caution, it is all but certain that the human species will be extinct in very short order.”

Even though very smart people disagree over whether this AI will ever exist, the concept of a science-fiction dystopia is simultaneously terrifying and alluring. It’s easy to imagine a Terminator-like world where machines do battle with their human creators and think of it as both unlikely to happen in our lifetimes and also inevitable. And this can make it hard to think about taking steps to stop it from happening. At least one study has found that people are worried about smart machines killing them.

“In our current society, automation pushes people out of jobs, making the people who own the machines richer and everyone else poorer. That is not a scientific issue; it is a political and socioeconomic problem that we as a society must solve,” wrote scientist Arend Hentz. “My research will not change that, though my political self – together with the rest of humanity – may be able to create circumstances in which AI becomes broadly beneficial instead of increasing the discrepancy between the one percent and the rest of us.”